This
car measures just 5 1/2 inches in length. It was sold as a remote
control car for $19.95 at Fry's Electronics here in Phoenix. Powered
by 4 AAA batteries, it has a small dc motor and a very interesting steering
mechanism.

After
gutting the original electronics, a piece of circuit board was cut to size
and mounted with one screw. The circuit board is pad-per-hole type
and the wiring on the bottom is done with tiny pieces of 30 guage (wire
wrap) wire soldered between points.

A check of the schematicshows several intersting features.
Visual detection is done with a pair of (matched) photocells.
This type of cell works at even very low light levels. By using
a pair in series feeding a 3 level comparator circuit, light sources can
be determined to be from left, right, or center. The photo
cells are physically located to 'look' through a hole drilled in the black
plastic windshield.

The motor drive circuit has an adjustable
current level detector. This detects motor 'stalls' and is
used to determine when an object has been hit.

To
save power in 'sleep' mode, the PIC powers down the entire external
circuit (the op-amp and associeated resistor networks) when not needed.

It was dificult
to get a good photo of the steering mechanism, so check the drawing.
A permanent magnet 'floats' on a pair of pivots and is held centered by
being attracted to a fixed set of metal pole pieces. When
power is applied to the solenoid, the pole pieces move the magent to the
left or right. Not really good for proportional control, but
a damn nifty way to steer.

This is an ongoing project to see how
'smart' this device can be made to behave. The current state of
the program is available as usual here.